Question

Pascal grammar for YACC and Lex

Asked by: crazyfacka

I'm in need to build a grammar interpreter for a language similar to Pascal using tools like YACC and Lex. I have found this on the internet: http://www.moorecad.com/standardpascal/yacclex.html

The problem resides in the fact that I cannot generate any type of output even with a simple Hello World program.

Could someone help me in making this thing work?

Thank you :)

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Asked On
2009-05-31 at 11:40:04ID24451915
Tags

pascal

,

grammar

,

yacc

,

lex

Topics

Parsers

,

Pascal Programming Language

,

Miscellaneous Programming

Participating Experts
2
Points
500
Comments
5

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Answers

 

by: mlmccPosted on 2009-05-31 at 13:10:41ID: 24513741

DO you have YACC and LEX?

mlmcc

 

by: crazyfackaPosted on 2009-05-31 at 13:41:27ID: 24513847

Yes I do.
And to compile it, I do the following:

lex pascal.l && yacc -d pascal.y && gcc -o gpascal y.tab.c lex.yy.c -ll -ly

But then, when I do something like "./gpascal < some_file.pas", nothing happens.

Thanks

 

by: mlmccPosted on 2009-05-31 at 14:30:15ID: 24514043

You need to add the code generation but it has been too long since I have done it.

There is a manual and example here

http://epaperpress.com/lexandyacc/

mlmcc

 

by: mrjoltcolaPosted on 2009-06-16 at 21:43:36ID: 24644884

Well the main problem is the grammar files you downloaded are rules without code.

The lex grammar will return tokens to the parser.
The parser will parse the tokens.

There is no code in there to print anything.

If you want to see what is happening at least add some printf() statements to some of the rules.

Example, below in the yacc grammar, do this change. Proceed with other rules.

The whole point of the rules is to allow you to build an abstract syntax tree, and then use that tree to generate code after the parse is done.

program : program_heading semicolon block DOT
 ;
 
--CHANGE TO--
 
program : program_heading semicolon block DOT
 {
     printf("program rule\n");
 }
 ;
                                              
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